The invention relates to a system and method for controlling gear shifts in a vehicle power train that includes an engine and an automatic transmission capable of producing multiple gear ratios.
Because shift quality control in automatic transmissions for motor vehicles is attempted using incomplete information from power train sensors, the quality of gear shifts, often called shift feel, produced by automatic transmissions operating under electronic control that employ conventional control strategies often lacks the desired smoothness. There is a continual need to minimize the torque disturbance at the output shaft of an automatic transmission caused by gear shifts. This disturbance often produces noise, vibration and harshness, which is felt by vehicle occupants.
Currently, the primary sensor information used in gear shift control is the transmission input speed and output speed. This information is indirectly used to infer and to control the transmission output torque during gear shifts, which occur as a result of coordinated engagement and disengagement of hydraulically actuated clutches and brakes that alternately connect and release components of planetary gearsets and layshaft gearing. Using control techniques conventionally applied to automatic transmission shift control, the slipping torque capacity of those clutches and brakes is adjusted in real time with reference to speed sensor information.
There is a continual need to minimize the disturbance at the output shaft of an automatic transmission caused by gear shifts. Shift feel can be improved by employing information from an additional sensor, an output shaft torque sensor (OST), which produces a signal representing the actual torque at the transmission output. The new OST sensor in combination with input torque control provide significantly improved shift feel control compared to the results produced by conventional hardware, control strategies, and calibration development techniques currently used for this purpose.
For most gear shifts produced automatically under electronic control, a control employing OST sensor information will produce an output torque magnitude after the gear shift that is equal to the output torque before the shift, eliminate output torque holes during the torque phase of each gear shift, and avoid output torque disturbances during the inertia phase of each gear shift.
Gearshift smoothness is achieved by directly sensing and controlling the power train parameters that the vehicle operator and other occupants actually feel. The resulting output torque it produces stays constant and on-target because output torque is not added or subtracted when decelerating or accelerating engine input inertia torque during upshifts and downshifts. Output torque sensing completes the information required to provide the true, real-time control of gear shift quality, long desired in transmission shift control.